Question

If the first term of an ap is -5 and the common difference is 2,then the sum of the first 12 terms is.............

Answer 1

Solution:

Given - First term in an A. P.= -5

common difference =d= 2

To find: Sum of first 12 terms =?

Sn = n/2 [2a +(n-1)d]

S12 =12/2[ 2 ×(-5)+(12-1)2]

S12 = 6(-10 + 22)

S12 = 6+10

S12=18.

Therefore the sum of first 12 terms of A.P. is 18